The present invention relates to initiators and detonators generally and to hot-wire initiators in particular.
The modem automobile requires many electronic initiators for activating various safety systems. Most well known are airbags of various types, but other devices requiring an initiator include seatbelt tensioners and hood elevators used to reduce pedestrian fatalities. Because some fifteen to twenty million vehicles are sold each year in the United States, and each vehicle may have many initiators, the total number of ignition devices for gas generators may soon be in the hundreds of millions per year. High reliability, low cost and minimal environmental contamination are also important consideration for these devices. Environmental contamination caused by toxic-metal-based primary explosives is of particular concern, even though the quantities used in a single detonator are minute. The gases produced by the initiation charge can be introduced into the passenger compartment where respiration by the passengers provides at least a theoretical concern for toxic metal exposure. A growing sensitivity to possible toxic metal contamination has also resulted in regulations forever more tightly controlling the use of toxic metals compounds such as those containing lead and mercury.
What is needed is an initiator for gas generators which is of low cost, reliable, and constructed without toxic metals compounds.
The initiator of this invention comprises a circuit board having two copper traces and a bridge resistor of Nichrome(copyright) or tantalum nitride mounted across the copper traces at one end of the board. A gap in the circuit board is formed between the copper traces where the resistor is positioned. At the other end of the circuit board wire leads or pins are joined to the wire traces. A zener diode is placed between the wire leads and a bridge resistor. The zener diode functions as a short across the copper traces when they apply a voltage above the all-fire voltage by more than a selected amount, such as results when a static electrical charge is applied to the wire leads. Immediately before the wire leads reach the circuit board they are passed through a ferrite core which serves to block high frequency signals which might cause premature ignition or detonation. The wire leads, the ferrite core, and the circuit board, excluding the end of the board to which the bridge resistor is mounted, is insert molded into a body of glass filled nylon 6,6. The nylon body, which is generally cylindrical in shape, mounts to a cylindrical soft aluminum can, which covers the bridge resistor. The aluminum can is bonded to a circumferential groove formed in the nylon body. The bond forms a hermetic seal between the aluminum can and the nylon body. Before the aluminum can is bonded in place the bridge resistor is covered with a primary explosive which is free of lead and mercury such as zirconium potassium perchlorate and the can is filled with gas generating granules such as 5-aminotetrazole. The gas generator granules do not need to be in direct contact with the initiation charge although they may be depending on the orientation of the initiator. The initiator is of the hot-wire type characterized by a rapid burning or deflagrating. This is in contrast to initiators that trigger an explosive with a supersonic detonation wave.
It is a feature of the present invention to provide an initiator of lower-cost.
It is another feature of the present invention to provide an initiator which does not contain toxic metals compounds.
It is a further feature of the present invention to provide an initiator which is protected against radio frequency and electrostatic discharge.
Further features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.